Structure for plastic encapsulation of semiconductor devices

ABSTRACT

An improvement in a plastic encapsulating process for semiconductor devices, wherein parts of a sheet-like thin insert are embedded in plastic material injected into cavities in a two-part mold, said insert being loaded or positioned on the cavity part of said mold, characterized in that at least either a projected or recesses portion, and correspondingly either a recessed or projected portion, have been in advance constructed respectively on each side edge of said insert and on said cavity part of the mold near the injection gate therein contacting each other so as to prevent an outflow of plastic material from said injection gate along a peripheral gap created between said side edge of the insert and the cavity part of the mold any further than their contacting point which acts as a stopper in said gap, producing an undesirable channel for plastic material to flow.

United States Patent Sakamoto et al.

[451 May 2,1972

[54] STRUCTURE FOR PLASTIC ENCAPSULATION OF SEMICONDUCTOR DEVICES [72]Inventors: Yuzaburo Sakamoto; Keizo Otsuki, both of Tokyo, Japan [73]Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: July 10, 1969 [21]Appl. No.: 840,634

[30] Foreign Application Priority Data July 10, 1968 Japan ..43/47752[52] U.S. Cl ..249/84, 18/5 E, 18/36, 18/42 D, 18/DIG. 10, 249/96,264/272 [51] Int. Cl. ..B29f 1/06 [58] Field of Search ..249/84, 85, 96,83; 18/42 D, 18/36, DIG. 29, DIG. 10,1 D, 5 E, 30 WC;

[56] References Cited UNITED STATES PATENTS 2,369,291 2/1945 Frank..18/36 Primary Examiner.l. Spencer Overholser Assistant Examiner-Ben D.Tobor Att0rneyCraig, Antonelli and Hill ABSTRACT An improvement in aplastic encapsulating process for semiconductor devices, wherein partsof a sheet-like thin insert are embedded in plastic material injectedinto cavities in a twopart mold, said insert being loaded or positionedon the cavity part of said mold, characterized in that at least either aprojected or recesses portion, and correspondingly either a recessed orprojected portion, have been in advance constructed respectively on eachside edge of said insert and on said cavity part of the mold near theinjection gate therein contacting each other so as to prevent an outflowof plastic material from said injection gate along a peripheral gapcreated between said side edge of the insert and the cavity part of themold any further than their contacting point which acts as a stopper insaid gap, producing an undesirable channel for plastic material to flow.

10 Claims, 7 Drawing Figures Patented May 2, 1972 3,659,821

2 Sheets-Sheet l INVENTORS YUZABURO SAKAMOTO 0nd KEIZO oTSUKl 4 W MyATTORNEY S Patented May 2, 1972 3,659,821

2 Sheets-Sheet 2 INVENTOR$ YUABMRO Moro 4 EI'LO O'TSHK'L Q a am a l/ 1ATTORNEY) BACKGROUND OF THE INVENTION Field of the Invention The presentinvention relates to plastic encapsulation of semiconductor devices.More specifically, it relates to an improvement in the structure of asheet-like metallic insert and two-part mold used in a plasticencapsulating process wherein parts of said insert are embedded inplastic material injected into cavities of said mold after said inserthas been loaded or positioned on the cavity part of said mold.

Description of the Prior Art For manufacturing small electronic devices,there is required a plastic encapsulating process wherein parts of asheet-like metallic insert are embedded in plastic material while otherparts of said insert are permitted to extend out of the plastic materialto serve as electrode leads. Transfer molding, utilizing a two-part moldto embed desired parts of a sheet-like metallic insert, is much employedfor the aforementioned plastic encapsulating process.

In order to carry out the afore-mentioned process successfully to obtaindesirable and satisfactory electronic devices, however, the structure ofthe sheet-like metallic insert and the cavity part of the two-part moldmust be very accurately constructed. Otherwise, since freely runningplastic material is commonly used in transfer molding, a phenomenonresults wherein an outflow of plastic material occurs through a smallperipheral gap between said insert and cavity part of the mold near theinjection gate where the injection pressure is especially high.Therefore, as a result of an outflow of plastic material intounprescribed and undesired spots, the injection pressure decreases withthe resulting occurrence of inferior molding. To prevent an outflow ofplastic material, it may be possible to construct the metallic insertand the two-part mold with sufficient accuracy to prevent leaks, butsuch highly accurate construction of the metallic insert and thetwo-part mold, and especially the metallic insert, can be achieved onlyat high cost. Thus, it is difficult to achieve such ends within thelimits of commercial practicality.

SUMMARY OF THE INVENTION Therefore, it is an object of the presentinvention to achieve by a process of transfer molding a successfulplastic encapsulation of small electronic devices that are satisfactory.

It is a further object of the present invention to keep the cost of thesubject process low so that the present invention may be well utilized.

According to the present invention, the foregoing and other objects areaccomplished by a configuration of the metallic insert and the two-partmold such that an outflow of plastic material from the injection gatealong a gap created between the side edge of said insert and the cavitypart of the two-part mold at the time of loading the former on thelatter is stopped at the contacting point of these elements with eachother which acts as a stopper in said gap, providing an undesirablechannel for plastic material to flow.

Therefore, in order to provide the above-mentioned contacting point ofthe metallic insert and the cavity part of the two-part mold with eachother, according to the present invention, either a projection or arecess is constructed on each side edge of said insert andcorrespondingly either a recess or a projection is constructed on saidcavity part of the mold near the injection gate therein.

The plastic encapsulating process according to the present inventionapplies to the manufacture of small electronic devices and especially ofsemiconductor integrated circuit devices.

BRIEF DESCRIPTION OF THE DRAWING The present invention may be betterunderstood by reference to the following detailed description of aspecific embodiment thereof taken in conjunction with drawing wherein:

FIG. 1 is a cross section showing the positional relationship of atwo-part mold, an insert, and plastic material.

FIG. 2 is a partial perspective view of the cavity part of a two-partmold and a metallic insert used in the plastic encapsulating processaccording to the present invention.

FIG. 3 shows a lead-frame as an insert used in the plastic encapsulatingprocess according to the present invention.

FIGS. 4a through 4d show enlarged views of parts of a leadframe shown inFIG. 3 and the cavity part of a two-part mold.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the presentinvention, as shown in FIG. 1, a two-part mold consisting of the plungerpart 1 and the cavity part 2 is used to embed a part of a metallicinsert 3 in plastic material 4.

In FIG. 2, a lead-frame 3 for manufacturing semiconductor integratedcircuit devices is used as an insert according to the present invention.About 0.25:0.02 mm thick cobalt sheet is stamped out into the properpattern for the lead-frame 3. Then, the electrode leads-to-be 16, l7, l8and 19 are properly connected through metallic thin wires (not shown) toa semiconductor pellet (not shown) placed on a part 15 of the lead-frame3. The part 15 and at least a part of each electrode lead near the part15 are generally plated with gold.

The abovementioned lead-frame 3 has an indented portion or a projectionand recess, circled and denoted by b in FIG. 2, in the form of anadjacent tooth and gap constructed on a side edge thereof according tothe present invention. Then, the lead-frame 3 is loaded or placed on thesurface 5 of the cavity part 2 of the two-part mold which also has anindented portion or a projection and a recess, circled and denoted by bin FIG. 2, in the form of an adjacent gap and tooth constructed in awall of the intercellular cavity thereof corresponding to that of theprojection and recess portion b of the lead-frame 3.

After the two-part mold is closed, that is the plunger part 1 coincideswith the cavity part 2 at the surface 6 thereof, a certain plasticmaterial is transferred into a cavity 9 through transfer guide 7 andgate 8 to embed a part of the lead-frame 3. An epoxy resin is commonlyused for the aforementioned plastic material. In the embodiment of thepresent invention, SCM-ll Hysol (epoxy resin compounds and amine andanhydride hardners) is used. It is desirable that the spiral flow ofepoxy resin is 30 36 inches with the minimum of 21 inches. Test forspiral flow is by the method of Epoxy Molding Materials Institute, theSociety of the Plastics Industry, Inc., 250 Park Avenue, New York, NewYork 10017. Among several molding processes, transfer molding is appliedfor the above process and performed at the temperature of C fi" for thecure time of 2.5 minutes in the embodiment of the present invention. Inthe aforementioned transfer molding, transfer pressure must be about 200psi with the minimum of 40==50 psi and clump pressure 2,000 psi.

When the lead-frame 3 is placed in the intercellular cavity of thecavity part 2 of the two-part mold, there are usually peripheral gaps10, as shown in FIGS. 4a through 4d, between the side edges of thelead-frame 3 and the walls of the intercellular cavity unless thelead-frame 3 and cavity part 2 of the mold are constructed in a highlyaccurate manner at increased cost. In the present invention, however,the gaps 10 are cut off at points of contact of the indented portions 1l, 12, 13 and 14 of the lead-frame 3 and cavity part 2 of the mold.Thus, the interengaging tooth and gap combinations serve to cut shortthe peripheral flow path for the plastic material.

A thin metal sheet is stamped out into a pattern of lead frame 3 withvarious indented portions on the subtending side edges as shown in FIG.3. A rolled thin metal sheet may be cut into a desired size of alead-frame in conveyance if the indented portions are such that one sideedge is set against the opposite side edge. It should be noted also thata lead-frame need not have all the indented portions shown in FIG. 3 butmay have only a projected or recessed portion on each side edge. On theother hand, additional indented portions may also be provided, so as toprovide interengaging tooth and gap combinations on all four sides ofthe mold.

When a fluid epoxy resin is transferred into cavities 9 (only one ofwhich is shown in FIG. 2) in the two-part mold through transfer guide 7and gate 8, the lead-frame 3 may be pushed by the transfer pressure ofepoxy resin against a wall of the intercellular cavity opposite of thetransfer gate 8 of the cavity part 2 of the mold. The lead-frame 3,however, is stopped from being pushed further at points of contact ofthe above-mentioned indented portions 11, 12, 13 and 14 as shown inFIGS. 4a, 4b, 4c and 4d, and at the same time contact points of highpressure are created between the interengaging teeth and gaps to preventflow of material thereby.

In FIGS. 4a, 4b, 4c and 4d, it is assumed that the lead-frame 3 ispushed by the transfer pressure of the epoxy resin from below. FIG. 4ashows that a projected or tooth portion 11 of the lead-frame 3 is incontact with the upper side of a recessed or gap portion 12 of thecavity pan 2; FIG. 4b shows the same; FIG. 40 shows that the lower sideof a recessed or gap portion 13 of the lead-frame 3 is in contact with aprojected or tooth portion 14 of the cavity part 2; and FIG. 4d showsthat a projected or tooth portion 11 and the lower side of a recessed orgap portion 13 of the lead-frame 3 are in contact respectively with theupper side of a recessed or gap portion 12 and a projected or toothportion 14 of the cavity part 2.

Unless the configuration of the lead-frame 3 and the cavity part 2 arehighly accurate, there are gaps created between the side edges of thelead-frame 3 and the walls of the intercellular cavity of the cavitypart 2 of the mold, as shown in FIGS. 4a through 4d. A part of the epoxyresin, therefore, runs into gaps 10 since the epoxy resin used in theprocess is freely running. The foregoing phenomenon is the beginning ofan outflow of epoxy resin into undesired spots which causes a fall inthe transfer pressure.

According to the present invention, however, the undesira ble channelfor resin flow is cut into pieces by points of contact of the indentedportions 11, 12, 13 and 14 of the leadframe 3 and cavity part 2 of themold, as shown in FIGS. 4a through 4d. Thus, the above-mentioned outflowof epoxy resin into gaps 10 is stopped short, so that the transferpressure is not caused to fall and the encapsulation of the lead-frame 3is satisfactorily completed.

As described above with reference to the embodiment according to thepresent invention, it is possible to prevent an outflow of plasticmaterial in gaps between an insert and the cavity part of a two-partmold further than a constructed point of the insert and cavity part ofthe mold in a transfer molding process for an encapsulation of theinsert with plastic material. Transfer pressure does not fall muchduring the process, and a successful molding is achieved to obtainsatisfactory and desirable electronic devices.

While the invention has been specifically shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that changes and modifications may be madetherein without departing from the spirit and scope thereof.

We claim:

1. In combination, a thin metallic insert having inside parts and aframe for holding the inside parts unitarily, and a mold having a spacefor receiving the frame of said metallic insert, a cavity correspondingto said inside parts of the insert and gate means for injecting fluidplastic material into said cavity of the mold to embed said inside partsof the insert in plastic material, wherein the improvement comprisesfirst\and second means provided on said frame of said insert and saidmold, respectively, for preventing flow of said fluid plastic materialalong a peripheral gap formed between said frame and the inner wall ofsaid space facing said frame, each of said first and second meanscomprising at least one adjacent tooth and gap combination positioned sothat the tooth of one combination engages with the gap of the othercombination.

2. The combination of claim 1 wherein said first and second means arepositioned on opposing portions of said frame and said mold,resgectiyely, nearsaid gate means.

3. The com matron of claim 1 wherein said first and second means eachcomprise plural spaced tooth and gap combinations provided alongopposite sides of said frame.

4. The combination of claim 3, wherein said gate means is provided alongone side of said mold adjacent a side of said frame which is transverseto said opposite sides on which said tooth and gap combinations areprovided so that the force of the injected plastic material against saidmetallic insert causes said teeth and gaps to form contact points.

5. In combination, a thin metallic insert having inside parts and aframe for holding the inside parts unitarily, and a mold having a spacefor receiving said frame of the metallic insert, a cavity correspondingto said inside parts of the insert and gate means for injecting fluidplastic material into said cavity of the mold to embed said inside partsof the insert in plastic material, wherein said metallic insert has atleast one combination of a projection and a recess formed along a sideedge of the frame of said insert so as to face the inner wall of saidmold when said insert is positioned in the space of said mold, and saidmold has a combination of a recess and a projection corresponding to andengaging with said projection and said recess of said insert wherebyleakage of the fluid plastic material flowing through said gap isstopped by the corresponding projection-recess combinations.

6. The combination of claim 5, wherein said insert has at least onecombination of a projection and a recess on each side edge of the framethereof, and said mold has at least one combination of a recess and aprojection at the position thereof corresponding to the respectivecombination of the projection and the recess.

7. In combination, a thin metallic insert having inside parts and aframe for holding the inside parts unitarily, and a mold having a spacefor receiving said frame of the metallic insert, a cavity correspondingto said inside parts of the insert and gate means for injecting fluidplastic material into said cavity of the mold to embed said inside partsof the insert in plastic material, wherein said metallic insert has atleast a projected portion on one and a recessed portion on the otherside edge of the frame of said insert so as to face the inner wall ofsaid mold when said insert is positioned in the space of said mold, andsaid mold has a recessed and a projected portion on portions thereofrespectively corresponding to and engaging with said projected and saidrecessed portion of the insert, whereby leakage of the fluid plasticmaterial flowing through said gap is stopped by the correspondingprojection-recess combinations.

8. In combination, a thin metallic insert having inside parts and aframe for holding the inside parts unitarily, and a mold having a spacefor receiving said frame of the metallic insert, a cavity correspondingto said inside parts of the insert and gate means for injecting fluidplastic material into said cavity of the mold to embed said inside partsof the insert in plastic material, wherein said frame of the metallicinsert constitutes a closed enclosure surrounding said inside parts andhas an indented portion at an outer side edge thereof so as to face theinner wall of said mold when said insert is positioned in the space ofsaid mold, and said mold has an indented portion corresponding to andengaging with said indented portion of said insert, whereby leakage ofthe fluid plastic material flowing through said gap is stopped by theengaged combination of the indented portions.

9. The combination of claim 8, wherein said insert has at least aprojected portion on one and a recessed portion on the opposite sideedge of the frame thereof, and said mold has at least a projectedportion and a recessed portion on positions thereof respectivelycorresponding to said projected and recessed portions of the insert.

10. The combination of claim 8, wherein said insert has at least aprojection-recess portion on each side edge of the frame and said moldhas at least a recess-projection portion at positions thereofcorresponding to said projection-recess portions of the insert.

1. In combination, a thin metallic insert having inside parts and aframe for holding the inside parts unitarily, and a mold having a spacefor receiving the frame of said metallic insert, a cavity correspondingto said inside parts of the insert and gate means for injecting fluidplastic material into said cavity of the mold to embed said inside partsof the insert in plastic material, wherein the improvement comprisesfirst and second means provided on said frame of said insert and saidmold, respectively, for preventing flow of said fluid plastic materialalong a peripheral gap formed between said frame and the inner wall ofsaid space facing said frame, each of said first and second meanscomprising at least one adjacent tooth and gap combination positioned sothat the tooth of one combination engages with the gap of the othercombination.
 2. The combination of claim 1 wherein said first and secondmeans are positioned on opposing portions of said frame and said mold,respectively, near said gate means.
 3. The combination of claim 1wherein said first and second means each comprise plural spaced toothand gap combinations provided along opposite sides of said frame.
 4. Thecombination of claim 3, wherein said gate means is provided along oneside of said mold adjacent a side of said frame which is transverse tosaid opposite sides on which said tooth and gap combinations areprovided so that the force of the injected plastic material against saidmetallic insert causes said teeth and gaps to form contact points.
 5. Incombination, a thin metallic insert having inside parts and a frame forholding the inside parts unitarily, and a mold having a space forreceiving said frame of the metallic insert, a cavity corresponding tosaid inside parts of the insert and gate means for injecting fluidplastic material into said cavity of the mold to embed said inside partsof the insert in plastic material, wherein said metallic insert has atleast one combination of a projection and a recess formed along a sideedge of the frame of said insert so as to face the inner wall of saidmold when said insert is positioned in the space of said mold, and saidmold has a combination of a recess and a projection corresponding to andengaging with said projection and said recess of said insert wherebyleakage of the fluid plastic material flowing through said gap isstopped by the corresponding projection-recess combinations.
 6. Thecombination of claim 5, wherein said insert has at least one combinationof a projection and a recess on each side edge of the frame thereof, andsaid mold has at least one combination of a recess and a projection atthe position thereof corresponding to the respective combination of theprojection and the recess.
 7. In combination, a thin metalLic inserthaving inside parts and a frame for holding the inside parts unitarily,and a mold having a space for receiving said frame of the metallicinsert, a cavity corresponding to said inside parts of the insert andgate means for injecting fluid plastic material into said cavity of themold to embed said inside parts of the insert in plastic material,wherein said metallic insert has at least a projected portion on one anda recessed portion on the other side edge of the frame of said insert soas to face the inner wall of said mold when said insert is positioned inthe space of said mold, and said mold has a recessed and a projectedportion on portions thereof respectively corresponding to and engagingwith said projected and said recessed portion of the insert, wherebyleakage of the fluid plastic material flowing through said gap isstopped by the corresponding projection-recess combinations.
 8. Incombination, a thin metallic insert having inside parts and a frame forholding the inside parts unitarily, and a mold having a space forreceiving said frame of the metallic insert, a cavity corresponding tosaid inside parts of the insert and gate means for injecting fluidplastic material into said cavity of the mold to embed said inside partsof the insert in plastic material, wherein said frame of the metallicinsert constitutes a closed enclosure surrounding said inside parts andhas an indented portion at an outer side edge thereof so as to face theinner wall of said mold when said insert is positioned in the space ofsaid mold, and said mold has an indented portion corresponding to andengaging with said indented portion of said insert, whereby leakage ofthe fluid plastic material flowing through said gap is stopped by theengaged combination of the indented portions.
 9. The combination ofclaim 8, wherein said insert has at least a projected portion on one anda recessed portion on the opposite side edge of the frame thereof, andsaid mold has at least a projected portion and a recessed portion onpositions thereof respectively corresponding to said projected andrecessed portions of the insert.
 10. The combination of claim 8, whereinsaid insert has at least a projection-recess portion on each side edgeof the frame and said mold has at least a recess-projection portion atpositions thereof corresponding to said projection-recess portions ofthe insert.